1. Field of the Invention
The present invention relates to a method of detecting and analyzing impurities contained in a liquid sample with a high level of precision.
2. Description of the Related Art
A known method of detecting and analyzing impurities in a liquid sample will be described with reference to FIG. 9. A liquid sample 1 is contained in a pipette 2. A substrate 3 is disposed below the pipette 2 so that the liquid sample 1 can be dropped on the substrate 3 and be transferred thereby to an analyzing device, etc.
The substrate 3 has previously been subjected to the following treatment. Namely, it is cleaned by soaking it in a cleaning liquid which is, for instance, a hydrofluoric-acid based acid or a mixture of sulfuric acid and nitric acid, thereby removing any foreign matter attached to the surfaces of the substrate 3. After the cleaning, the substrate 3 is dried by, for instance, applying thereto a jet of nitrogen gas.
A suitable amount of the liquid sample 1 is discharged from the pipette 2 and is dropped on the surface of the substrate 3 which has been cleaned and dried in the above fashion. Thereafter, the liquid sample 1 on the substrate 3 is allowed to dry or is dried by heating the substrate 3 in a heating device (not shown). By this drying, impurities contained in the liquid sample 1 become attached to the surface of the substrate 3.
Subsequently, the substrate 3 is placed in an ordinary solid analyzing device (not shown) in which impurities attached to the surface of the substrate 3 are analyzed.
The known method is adapted to detect and analyze impurities contained in the liquid sample 1 in the above-mentioned manner. This known method of detecting and analyzing impurities, however, involves the following disadvantages.
First, with the known method, there is a risk that foreign matter which may possibly be contained in the cleaning liquid used to clean the substrate 3 may become attached to the substrate 3 while it is cleaned. Foreign matter which is not in the cleaning liquid may also become attached to the substrate 3 during the cleaning.
Second, since the substrate 3 is simply soaked in the cleaning liquid according to the known method, there is a risk that foreign matter on the surfaces of the substrate 3 may not be removed to a sufficient extent and may remain attached to the surface.
Thirdly, with the known method, there is a risk that, during the drying of the liquid sample 1 which has been dropped on the substrate 3, foreign matter may become mixed with the liquid sample 1.
Lastly, if the substrate 3 is heated according to the known method so that the liquid sample 1 dropped on the substrate 3 can dry quickly, there is a risk that certain types of liquid samples 1 may decompose at the temperatures used to heat the substrate 3. Thus, the heating process has to be conducted carefully in this respect.
Because of these disadvantages, it has been difficult to achieve high levels of precision in the detection and analysis of impurities contained in a liquid sample by using the known method.